Don't do unnecessary queries when listing subprojects

This together with:
- #6867
- #6865
- #6864

reduces a lot of queries and without changing the current UI.

This is a benchmark using the django debug toolbar:

Before: 138 queries with 7 subprojects, 17 queries per each additional subproject

With all the changes: 28 queries with 7 subprojects, 1 query per each additional subproject

Author: stsewd

readthedocs/projects/views/private.py

@@ -2,6 +2,8 @@
 
 import csv
 import logging
+from urllib.parse import urlparse
+from readthedocs.core.resolver import resolve, resolve_path
 
 from allauth.socialaccount.models import SocialAccount
 from django.conf import settings
@@ -462,8 +464,36 @@ class ProjectRelationshipList(ProjectRelationshipMixin, ListView):
     def get_context_data(self, **kwargs):
         ctx = super().get_context_data(**kwargs)
         ctx['superproject'] = self.project.superprojects.first()
+        ctx['subprojects_and_urls'] = self.get_subprojects_and_urls()
         return ctx
 
+    def get_subprojects_and_urls(self):
+        """
+        Get a tuple of subprojects and its absolute URls.
+
+        All subprojects share the domain from the parent,
+        so instead of resolving the domain and path of each subproject,
+        we only resolve the path of each one.
+        """
+        subprojects_and_urls = []
+
+        main_domain = resolve(self.project)
+        parsed_main_domain = urlparse(main_domain)
+
+        subprojects = self.object_list.select_related('child')
+        for subproject in subprojects:
+            subproject_path = resolve_path(subproject.child)
+            parsed_subproject_domain = parsed_main_domain._replace(
+                path=subproject_path,
+            )
+            subprojects_and_urls.append(
+                (
+                    subproject,
+                    parsed_subproject_domain.geturl(),
+                )
+            )
+        return subprojects_and_urls
+
 
 class ProjectRelationshipCreate(ProjectRelationshipMixin, CreateView):
 

readthedocs/templates/projects/projectrelationship_list.html

@@ -48,7 +48,7 @@
       <div class="module-list">
         <div class="module-list-wrapper">
           <ul class="subprojects">
-            {% for subproject in object_list %}
+             {% for subproject, absolute_url in subprojects_and_urls %}
               <li class="module-item subproject">
                 <div class="module-title">
                   <a
@@ -58,8 +58,8 @@
                   </a>
                   <span>
                     <a class="module-info subproject-url"
-                      href="{{ subproject.get_absolute_url }}">
-                      {{ subproject.get_absolute_url }}
+                      href="{{ absolute_url }}">
+                      {{ absolute_url }}
                     </a>
                   </span>
                 </div>